The aim of this study was to identify informative progression markers by methylation analyses of eleven genes known to be methylated in breast tumours or breast cancer cell lines; ABCB1 [18], CDKN2A/p16INK4a [19], ESR1 [20], GSTP1 [21], IGF2 [22], MGMT [19], MLH1 [19], PPP2R2B [23], PTEN [24], RASSF1A [25] or displaying variation in breast cancer sub-type gene expression profiles; FOXC1. The gene discussed is ESR1; the disease is breast cancer.